Communication networks have been designed to deliver media content to recipients using cable, satellite, and mobile television. Delivery may be by unicast (one to one) or broadcast (one to many). In a subscription-based system, for example, in order to receive the content an Entitlement Management Message (EMM) is first delivered to a wireless device, also referred to as the subscriber unit. The EMM may be delivered using unicast or broadcast delivery. The EMM includes secret data, such as a logical key, which enables a user to access media content that has been protected, such as by encryption, so that only authorized users can access the content.
For new subscriptions and changed subscriptions, unicast EMM delivery is often a preferred method for connected devices. For example, in satellite and cable television services, a set top box is connected to the phone line in order to receive the EMM for initial activation. In contrast, media content services for wireless devices, such a mobile television, differ in that the device usually has connectivity through a cellular data service or an Internet service. This allows the new or changed subscription to take effect immediately.
For devices with no unicast connection, also known as unconnected devices, EMM delivery occurs via broadcast. In some cases, even with connected devices, broadcast delivery may be preferred. This may be true for subscription renewals, especially for subscriptions that require periodic renewal. For example, in a television service network the number of subscribers could be large, possibly in the millions. If an EMM were to be sent to each device individually the network would be too congested to successfully process the renewal subscriptions. Broadcast delivery allows the EMM to be addressed to any subscriber unit capable of receiving the broadcast, thus saving bandwidth.
In broadcast delivery in a mobile television network, the network repeatedly broadcasts the EMMs for the next subscription renewal period. The repetition rate is known as the cycle time. Cycle time is the period between two instances of broadcasting the EMMs destined for a given mobile station. The cycle time may be a function of the bandwidth and the number of subscribers. Thus, for example, if the number of subscribers is large and the amount of bandwidth allocated for the broadcast is limited, the cycle time may be longer.
Conventionally, EMM broadcast delivery in an existing mobile television network occurs while the user is watching content, the user's device tunes to the channel where the EMMs are being broadcast while the user is watching content. The mobile station receives all the EMMs broadcast during this time and processes them to determine the EMMs relevant to the user's device. The mobile television operator selects the cycle time such that if the user watches mobile television for a period of time during the day, the network will guarantee reception of the EMM with some probability. The network does not know when the user will turn on the mobile television application, nor how long the user will watch television. Because of this the EMM broadcast cycle time is typically small. Otherwise, the user may fail to watch content during the EMM cycle time because the unit does not have the most recent EMM available.
In the above case, given that the re-broadcast rate is high, one problem with this method of EMM delivery is consuming a significant amount of bandwidth. Mobile television broadcast bandwidth is quite expensive and operators wish to use as much bandwidth as possible to deliver content, which generates revenue. Another problem with the current EMM delivery mechanism is that while the user is watching content, the device needs to monitor the EMM channels over the air to see if its respective renewal EMM is being broadcast. This causes considerable device battery drain since the device must demodulate the flows in their respective channels and receive all the EMMs being broadcasted and then search for the ones relevant to the device.